The power MOSFETs used in the amplification stages of these systems are sometimes subject to electric shocks that can cause them to be damaged, or even destroyed. As an example, a power amplifier in a radiocommunication system is sometimes subject to abrupt changes of load impedance, for example when an antenna at the output of the amplifier is connected/disconnected or when there is a switch of spectral band in operation. When the system is in use, the accumulation of these electric shocks can degrade the reliability of the amplifier.
Moreover, during the optimization phase of the electronic systems, the amplitude of the electric current used may vary strongly because of the tests carried out on the system, thus rendering the components, notably the MOSFETs, vulnerable to destruction. Such destruction during the optimization phases generates significant additional costs, with certain power MOSFETs being particularly costly.
Many existing systems rely on the use of MOSFETs whose intrinsic characteristics make it possible to withstand fairly unfavorable operating conditions, without, however, being able to protect the MOSFET against certain incidents such as excessively high excitation currents. Some circuits have been proposed in order to protect the MOSFETs. Notably, it is known to associate with the MOSFET a circuit that behaves like a fuse, cutting the excitation current of the MOSFET in the event of a malfunction. However, the known circuits do not operate at radiofrequencies and/or require a large number of components.
The American patent published under the reference U.S. Pat. No. 6,856,200 for the company Marvell International Ltd. provides a protection circuit comprising a switching transistor acting as a switch between the gate of the MOSFET to be protected and the electrical ground, the switching transistor being placed in the closed position when a control signal is emitted to the drain of said switching transistor. However, when this switching transistor is placed in the open position, it acts as an undesirable capacitance between the gate of the MOSFET and the electrical ground, this capacitance disrupting the operation of the circuit comprising the MOSFET, notably at high frequencies.
The protection circuit should preferably neither affect the performance of the circuit comprising the MOSFET, nor restrict its operating ranges, in particular temperature-wise.